I wrote the following in response to an e-mail question asking about some verses in the Second Gospel:
My understanding is that Mark's Gospel is a fragmentary, incomplete, later account of secondhand recollections of some things Jesus did, which the collector ("Mark") did not really understand.
Mark's Gospel reads like somebody gathered many accounts of Jesus's life and sayings; and recorded them for posterity without trying to explain how they fitted together or what they meant.
Thus Mark is more accurate than Matthew or Luke (which were apparently compiled from some of the same sources, and/or from Mark itself), in that Mark is not imposing a single interpretative scheme on recollections; but at the same time Mark cannot stand alone.
Validly to understand Mark, and discern what in it is meaningful or valid and what is not, requires a perspective learned from the Fourth Gospel ("John").